As a method to detect the rotation angle of the rotor (motor shaft) of a motor, the method using the resolver is known. The resolver is a rotation detecting device detecting the rotation angle of the rotor based on the phase difference between the rotor coil and the stator coil. For example, a resolver includes: an excitation coil; a resolver rotor rotating with the motor shaft; and a detection coil. When, alternating current is applied to the excitation coil, electrical voltage whose amplitude corresponds to the rotation angle of the resolver rotor is generated in the detection coil. As such, based on the amplitude of the electrical voltage generated in the detection coil, the rotation angle of the rotor (the rotation angle of the resolver rotor, which is the rotation angle of the motor shaft) can be detected.
During detection of the rotation angle of the rotor with the resolver, error occurs depending on the mounting position of the resolver or the like. Several methods are proposed in order to correct the error (reduce the extent of the error).
For example, there is a method in which an error map corresponding to the rotation angle of the rotor to be detected by the resolver is generated in advance and the error is corrected by using the error map. The error map can be generated by performing the error-deriving operation relative to multiple rotation angles of the rotor. In the error-acquiring operation, the rotor is set to a certain specific angle, and difference between the set rotation angle (real rotation angle) and the rotation angle detected by the resolver.
Also, a rotation angle detection device is proposed in Patent Literature 1 (PTL 1). This rotation angle detection device disclosed in PTL 1 includes: a resolver that detect the rotation angle of the rotor of the motor to output a rotation angle signal; a rotation angle calculation unit that calculates the rotation angle of the rotor based on the rotation angle signal; EEPROM that has stored the offset angle and the amplitude of the higher-order sine wave components included in the errors of the rotation angles in advance; a higher-order sine wave component calculating unit that calculates the multiple higher-order sine wave components based on the rotation angles, the offset angles, and the amplitudes; and a rotation angle correction unit that calculates the correcting rotation angle by subtracting the multiple higher-order sine wave components from the rotation angles.
Because of the configuration described above, the rotation angle can be detected highly accurately without including errors.